Motor vehicles – Steering gear – With electric power assist
Reexamination Certificate
2000-06-26
2002-09-17
Hurley, Kevin (Department: 3611)
Motor vehicles
Steering gear
With electric power assist
C180S443000, C701S041000
Reexamination Certificate
active
06450287
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electric power steering controller for automobiles which causes a motor to generate torque for assisting the steering torque of a driver to assist the steering force of a steering system.
2. Description of the Prior Art
FIG. 40
is a block diagram showing the constitution of an electric power steering controller of the prior art disclosed by Japanese Laid-open Patent Application No. 7-186994, for example. In the figure, reference numeral
1
denotes a steering torque detector for detecting steering torque when a driver controls the steering wheel,
2
a steering torque controller for computing an assist torque signal based on the output of the steering torque detector
1
,
3
a damping compensator for computing a damping compensation signal based on the output of a motor speed detector
5
, and
4
an inertia compensator for computing an inertia compensation signal based on the output of a motor acceleration detector
6
. Denoted by
7
is a motor current decision unit for computing a target current signal from target torque which is the sum of an assist torque signal, damping compensation signal and inertia compensation signal, computed by a first adder
12
,
8
a decision unit for judging whether the output of the steering torque detector
1
and the output of the motor speed detector
5
have the same direction and outputting its decision result to the steering torque controller
2
, the damping compensator
3
and the inertia compensator
4
,
9
a motor drive unit for determining voltage to be applied to a motor
10
based on a difference obtained by a second adder
13
between a target current signal and a motor current value detected by the motor current detector
11
and applying the above voltage to the motor
10
, and
10
the motor for generating assist torque which is substantially proportional to a motor current value which changes according to the above applied voltage to drive a steering unit. Reference numeral
14
denotes a car speed detector for detecting car speed and outputting its detected car speed signal to the steering torque controller
2
, damping compensator
3
and inertia compensator
4
.
A description is subsequently given of the operation of the electric power steering controller of the prior art.
When the car driver controls the steering wheel, steering torque at this point is measured by the steering torque detector
1
and output to the steering torque controller
2
. The steering torque controller
2
computes an assist torque signal which is substantially proportional to the output signal of the above steering torque detector
1
and based on which the motor
10
is driven to assist the steering torque of the driver so as to reduce it.
At this point, the decision unit
8
judges whether the output of the steering torque detector
1
and the output of the motor speed detector
5
are the same. When they are the same, the damping compensator
3
and the inertia compensator
4
are not activated, the steering torque controller
2
determines target torque based on the assist torque signal which is determined based on the output of the steering torque detector
1
and a car speed signal from the car speed detector
14
, and the motor current decision unit
7
determines a motor drive current. When they are not the same, the steering torque controller
2
is not activated, target torque is determined based on the outputs of the damping compensator
3
and the inertia compensator
4
, and the motor current decision unit
7
determines a motor drive current. When the car speed is low at this point, the direction of target torque is made the same as the revolution direction of the motor and when the car speed is high, the direction of target torque is made opposite to the revolution direction of the motor. Therefore, when the driver turns the steering wheel, the steering torque of the driver is assisted to lighten torque required for steering. When the driver returns the steering wheel, the motor
10
is controlled such that the steering wheel is assisted to return to its starting point when the car speed is low and prevented from returning to its starting point at an excessive rotation speed when the car speed is high.
Generally speaking, the driver controls the steering wheel when turning a curved portion of a road or an intersection and returns the steering wheel to its starting point, making use of the spontaneous return force of the steering wheel generated by the road reaction torque of tires when returning to straight-line driving. However, since the road reaction torque of the tires is small when the driver controls the steering wheel slightly at a low car speed or a high car speed, the road reaction torque becomes smaller than friction torque in the steering unit, whereby the steering wheel does not return to its starting point in many cases at the time of returning to straight-line driving. Therefore, in this case, the driver must add torque to the steering wheel to return it to its starting point, thereby deteriorating a steering feeling.
In contrast to this, in the prior art, it is judged whether the output of the steering torque detector
1
and the output of the motor acceleration detector
6
are the same or not when the car speed is low, and a motor drive current is determined such that the motor
10
revolves in the same direction as the revolution direction of the motor when they are different, thereby improving the returnability of the steering wheel at a low car speed.
However, in the above prior art, when the driver controls the steering wheel with the small road reaction torque of the tires, for example, when the driver turns an intersection at a low speed or a gently curved portion of a road at a high speed, the steering wheel is stopped unless torque is added in a direction for returning the steering wheel, whereby the motor
10
does not revolve. Since the decision unit
8
cannot judge whether the output of the steering torque detector
1
and the output of the motor speed detector
5
are the same or not, it cannot determine a motor drive current for revolving the motor
10
in the same direction as the revolution direction of the motor and cannot improve the returnability of the steering wheel.
Further, since a motor drive current can be determined only to revolve the motor in a direction opposite to the revolution direction of the motor at the time of high-speed driving in the above prior art, the returnability of the steering wheel cannot be improved.
SUMMARY OF THE INVENTION
It is an object of the present invention which has been made to solve the above problems to provide an electric power steering controller which enables the steering wheel to be returned to its starting point without adding torque in a direction in which the driver returns the steering wheel when he/she controls the steering wheel with the small road reaction torque of the tires, for example, when he/she turns an intersection at a low speed or when he/she turns a gently curved portion of a road at a high speed.
According to a first aspect of the present invention, there is provided an electric power steering controller which comprises road reaction torque detection means for detecting road reaction torque received by tires from a road and road reaction torque addition control means for controlling the torque of a motor for assisting the steering torque of a driver based on road reaction torque detected by the road reaction torque detection means.
According to a second aspect of the present invention, there is provided an electric power steering controller which further comprises steering torque detection means for detecting the steering torque of the driver and steering assist control means for controlling the torque of the motor based on the output of the steering torque detection means.
According to a third aspect of the present invention, there is provided an electric power steering controller wherein the amount of control of the above road reaction torqu
Inoue Noriyuki
Kifuku Takayuki
Kurishige Masahiko
Nishiyama Ryoji
Wada Shunichi
Hurley Kevin
Leydig , Voit & Mayer, Ltd.
Mitsubishi Denki & Kabushiki Kaisha
Yeagley Daniel
LandOfFree
Electric power steering controller and control method thereof does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Electric power steering controller and control method thereof, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electric power steering controller and control method thereof will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2912937